Fabrication of incandescent lamps



Dec. 22, 1964 D. s. GUSTIN FABRICATION OF INCANDESCENT LAMPS Filed Aug. 9, 1961 FIGS 7 DANIEL S. GUSTIN INVENTOR. BA

ATTORN United States Iatent )fifice 3,162,499 Patented Dec. 22, 1964 3,162,499 FABRICATION F INCANBESCENT LAMPS Daniel S. Gusfiu, Loudonde. N.H., assignor to Sylvania Electric Products Inc, a corporation of Delaware Filed Aug. 9, 1961, Ser. No. 130,307 12 Claims. (Cl. 316-24) This invention relates to incandescent lamps and particularly to the fabrication of incandescent lamps having envelopes of a generally tubular shape.

In the manufacture of certain tubular lamps, it is neces sary to seal a longitudinally supported extending tungsten filament through both ends of a glass envelope and fill the lamp with an inert gas to retard the vaporization of the tungsten during subsequent illumination. A method commonly used to fabricate such lamps was to pinch seal the support filament through one end of the envelope, while the other end was temporarily plugged and while an inert gas was flowing into the envelope through a centrally appended exhaust tube. While continuing the flow of inert gas through the exhaust tube, the plug was removed, the other end of the envelope pinch-sealed and the exhaust tube then tipped off, thus sealing the lamp from the atmosphere and providing a filling of inert gas. The maintenance of an atmosphere of inert gas within the envelope during sealing operations is essential to prevent oxidation of the highly-heated filamentary components. Furthermore, the method concurrently provided an inert fill gas within the sealed lamp at a pressure of approximately one atmosphere.

While the above described method can be used to fabricate high quality lamps, a residual fused tip of the appended exhaust tube is always left on the envelope and in many applications, such fused tips are quite undesirable, because they affect the optical properties of the lamp. For example, when a lamp having a residual fused tip is used in a photo-copy machine, it has been found that the light is unevenly distributed upon the paper and since exact and critical limitations are placed upon the distribution of light in such machines, the work was not perfectly copied.

Accordingly, the primary object of my invention is the fabrication of a so-called tipless, tubular incandescent lamp, that is, one having no residual, fused exhaust tube tip on the outer surface of the envelope.

A feature of this invention is that during fabrication of the lamp, the inert fill gas is introduced through the open end of the tubular lamp envelope, rather than through an appended exhaust tube.

Another feature of this invention is that filaments and associated metal supporting parts are blanketed to prevent oxidation during heating and sealing operations by an inert gas which flows through substantially the enfire length of the envelope from one end to the other.

A further feature of this invention is that the inert gas which is used to blanket the filamentary components during sealing of one end of the tubular envelope emanates from a liquified pool of the inert gas within the envelope.

An advantage of this invention is that tubular lamps havin an inert fill gas are produced having no fused residual ends from tipped off exhaust tubes.

Many other advantages, features and objects of the present invention will become manifest to those conversant with the art, upon making reference to the detailed description which follows and the accompanying sheet of drawings in which a preferred procedural embodiment of a method of fabricating a generally tubular shaped incandescent lamp and filling it with an inert gas is shown and described, and wherein the principles of the present invention are incorporated by way of illustrative example.

The drawings are in the nature of flow sheets showing, together with the manipulative tools and the materials worked upon, the various successive steps in my process for preparing a so-called, tipless, tubular incandescent lamp. In each of the several figures of the drawing, similar numerical designations are indicative of similar elements. Of these drawings:

FIGURE 1 shows a tubular lamp envelope positioned in a pinch sealing device and being fired at one end to soften the glass. The other end of the tubular envelope is inserted within a schematically illustrated distribution head for filling the interior of the envelope with an inert gas, thus blanketing the heated filamentary components to prevent oxidation.

FIGURE 2 shows the sealed end of the lamp envelope inserted within a bath of liquified gas to condense the inert gas introduced through the schematically illustrated distribution head.

FIGURE 3 illustrates the partially sealed envelope after it has been removed from the bath of liquified gas and preparatory to making the final seal on the envelope. T he figure further shows boiling the pool of condensed liquid inert gas to provide the oxidation-preventing blanket.

FIGURE 4 is a later stage of the view shown in FIG- URE 3 and the figure illustrates the envelope while it is being heated and just before the final sealing.

FIGURE 5 illustrates the final sealing of the softened end of the tubular envelope.

FIGURE 6 is illustrative of a tubular incandescent lamp prepared according to the prior art.

FIGURE 7 is illustrative of a tubular incandescent lamp prepared according to the principles of my inven tion.

Briefly, the practice of my invention involves the fabrication of a filament sub-assemblycomprising an elongated coiled filament having a support of small sheets of molybdenum foil attached to lead-in wires associated with either end theerof and having additional lead-in wires attached to each sheet of foil. Small spacers generally prepared of tantalum are positioned about the tungsten filament every one or two inches along its length to pre vent sagging when the filament is inserted within the tubular glass envelope. In some instances where, for example, the filament is short or where non-sag wire is used, such spacers may be eliminated. After fabrication of the filament sub-assembly, it is positioned within a glass envelope usually prepared of a high silica content glass, such as quartz or vycor or in some cases, of a softer glass. The envelope is clamped in a press sealing machine and high temperature flames are directed at one end. Continually during this heating, a blanket of suitable inert fill gas is directed through the envelope over all metal parts to prevent their oxidation. When the glass is soft, a press seal is made, thereby sealing one end of the envelope. While still continuing the introduction of inert fill gas, the sealed end of the envelope is rapidly cooled in air and then immersed within a refrigerant or chilled within a suitable rapid chilling refrigerator. When using a liquid refrigerant, its boiling point generally must be below the boiling point of the inert fill gas and when using argon as the fill gas, liquid nitrogen may serve as the refrigerant. During chilling, a pool of liquified inert fill gas will form within the sealed end of the envelope and when a sufiicient quantity has been formed, the envelope is replaced in the glass sealing machine. The unsealed end is then heated to softening and the condensed pool of inert fill gas is allowed to gasify. When only the last vestiges of the pool remain, for example, about a drop, a press seal is made in the softened end of the internal pressures may be realized by leaving larger 3 quantities of liquid fill gas within the envelope before sealing. Irrespective of the internal gas pressure, the lamp produced has no residual exhaust tube tip on the surface of the envelope. I

In a more specific description, reference is made. to FIGURE lot the drawing. The first steps of fabricating the filament sub-assembly and positioning it within the envelope are not shown. A illustrated, a glass envelope 1 containing the elongated, coiled tungsten filament 3 supported on an associated'support 23 and spacers 4 is retained within clamps 5 of a sealing machine. The filament sub-assembly 3 is. suspended within the envelope from a clamp 19 which is positioned between a pair of open press sealers 6. A distribution head '7 having a line 8 from a source of fill gas (not shown) is positioned about one open end of the envelope to produce a fio-W of blanket- .ing, inert fill gas through the entire length of the envelope to prevent any oxidation of the metal parts. The pressure of the fill gas'within the envelope before the first seal should be just slightly above atmospheric to produce proper seals. When the envelope is properly positioned, a flame from burner 9 is directed at the open end of the envelope to soften the glass and when the glass is suificientlysoft press sealers 6 are closed and re-opened according to conventional glass sealing techniques.

The partially sealed envelope is then removed from clamps 5 of the sealing machine and the heated end is cooled in an air blast until moderately cool (not shown) and then partially immersed within a bath of liquid refrigerant Ztl, as shown in FIGURE 2. The depth of immersion is not critical, however we prefer tov immerse at least half of the envelope within the bath 20. During the cooling with the air blast and during the immersion within the bath 20, the distribution head 7 remains on the unsealed end of the envelope 1 to maintain the atmosphere of inert gas. After continued chilling, a pool ofliquified, condensed fill gas 21 will form within the envelope 1.

' I The choice of refrigerant for the bath 2@ will depend upon the choice of the fill gas, since to condense the fill gas it is essential that the boiling point of the refri erant be below the boiling point of the inert gas. When using argon as the blanketing fill gas, I have preferred the use of liquid nitrogen as the refrigerant, however other appropriate refrigerants such as helium, noen or some of the low boiling Freons may also be used. Although I prefer argon for the blanketing fill gas, the other inert gases such as helium, neon, xenon or krypton may be used and further, certain other gases inert or non-reactive with the filament or associated metal parts, such as nitrogen, have applicability and I may even introduce gases non-deleterious with the components of the lamp, such as a gasified 4 envelope 1 with the pool of liquified fill gas 21, is clamped in the sealing machine so that the open end may be sealed. The pool 21 is allowed to gasify and may even be aided in such gasification by heating with a flame from burner 32. Concurrently withthe gasification of the pool 21, a flame from burner 9 is directed at the unsealed end of the envelope 1 to'softe'n the glass and make ready for a press seal at that end. K

As shown in FIGURE 4, the gasification of the liquified fill gas is continued until but a very small quantity remains within the envelope 1. Conveniently, heating the liquid with the burner 32 serves to produce a visual reference for the appropriate time to seal the envelope 1, since as more and more of the liquid is gasified, the glass will change from transparent to cherry color and then to very bright shades of red. When theglass is very bright red and almost all of the liquid gasified, the press sealers 6 are quickly closed and opened and since the unsealed end I of the glass envelope 1 has already been softened by. the

fiazne from burner 9, an efficient and tight metal to glass seal about the filament supports comprising lead-in wire 22, the molybdenum foil (not shown) and the filament supporting lead-in wire will be made.

v The precise time of when to seal the open end of the envelope 1 is one of the most critical occasions in the entire operation, when a lamp having one atmosphere of fill gas is desired. The last of liquified fill gas must be tical considerations this may be varied by a factor of plus halogen, for example iodineor mixtures of iodine and nitrogen. I a p Suitable quantities of fill gas that are condensed'will vary depending upon the volume of the lamp envelope.

' For economy of operation, however, it is essential to condense as little fill gas as; possible, but there must be sufiicient quantities liquified to fill the envelope 1 entirely 'with gas upon subsequent gasification. Preferably, this minimum quantity is substantially exceeded because when the liquid changes to a gas, it tends to issue forth'frorn the open end of the envelope 1 and would be replaced by oxygen, which might result in an oxidizing atmosphere aroundthe metal'parts during sealing operations. When there is an excess of liquified fill gas, sufiicicnt time is available before entire gasification to allow the operator to position properly the envelope l'in the sealing machine.

' Theoretically, there is no maximum amount of fill gas which might e condensed within the envelope 1, however for practical considerations such as economy of operation, we preferto condense about /2 to 1 ml. When the desired quantity of fill gas is formed in the pool'Zl, the sealed and of theenvelope ii is removed from the bath 2t) and the distribution head 7 is removed: from the open end of the envelope 1. As shown in FIGURE 3,

or minus 0.1.

' While the invention'has particular application to lamps having one atmosphere of fill gas, it is also possible to modify the process and prepare lamps containing fill gas at super-atmospheric pressures, although the fabrication procedures are made more difiicult by such modifications. Particularly, larger predetermined quantities of liquified fill gas are left within the envelope before the second sealing and the second sealing can be carried on while the sealed end of the envelope 1 is immersed Within a refrigen ant pool and the then softened, sealed end of the envelope 1 is allowed to harden before the liquified fill gas is permitted to gasify. After gasification of the fill gas and hardening of the envelope, the increase of gas pressure will not form the objectionable bubble in the lamp, FIGURE 6 which is illustrative of the prior art; varies from FIGURE 7, which is illustrative of "a lamp produced according tothis invention by theinclusionfl a'residual exhausttube tip 61 on the surface of envelope tb. Allof the remaining elements can be identical. The filament support structureswnich are sealed within; the seal press of the envelope 64? comprise lead-in wires 74 molybdenum foil 64 and filament supporting wires 63 which are inserted within the core of filament 6'9 and can be identical to leadin wires'22 and 23, molybdenum foil 12 and filament supporting wires 18. When used spacers 4-can be of the same construction as those used in the prior art lamp and designated as 63. V p p 7 It is apparent that changes and modifications may be made" within the spirit and scope of the instant invention 'by those skilled inthe art. For example, the step of condensing the pool: of liquid fill gas may be modified: by eliminating condensationfand including a step of pouring ,a liquid fill gas into the envelope. Thus, it is my inten tionto be limited only by the spirit and scopeof the ap- 'pendediclaims. r

As my invention I claim.

1. In the process of fabricating a lamp having an envelope of generally regular and smooth outer surfaces the steps which comprise: flowing an inert gas into a glass envelope containing a filament, through an unsealed end of said envelope; refrigerating a seal end of said envelope to a temperature below the boiling point of said inert gas, thereby forming a pool of liquified inert gas therein; gasifying said pool of inert gas and heating said unsealed end of said envelope to soften the glass concurrently with said gasification; sealing the softened end of said envelope when substantially all of the pool of liquified inert gas is gasified, thereby forming an incandescent lamp containing a filling of inert gas at a pressure of about one atmosphere.

2. The process for fabricating a generally tubular incandescent lamp having a filament centrally sealed within an envelope having generally regular and smooth outer surfaces, the steps which comprise: flowing a fill gas through the length of a tubular glass envelope containing a centrally positioned filament, thereby forming an atmosphere which will prevent oxidation of metal parts contained therein; heating an end of said envelope to soften the glass and press sealing the softenend end about a support associated with one end of said filament a while maintaining the atmosphere of said fill gas; flowing fill gas into said envelope and forming a liquified pool of said fill gas within said envelope; gasifying said pool of liquified fill gas while concurrently heating the unsealed end of said envelope to soften the glass and press sealing the softened end of said envelope about a support associated with other end of said filament.

3. The process for fabricating a generally tubular incandescent lamp having a tungsten filament supported within an envelope and having generally regular and smooth outer surfaces, the steps which comprise: flowing an inert gas through the length of a tubular glass envelope containing a centrally positioned filament,-thereby forming an atmosphere to prevent oxidation of metal parts contained therein; heating an end of said envelope to soften the glass; press sealing the softened end of said envelope about a support associated with said filament While maintaining the atmosphere of said inert gas; flowing the inert gas through said envelope and refrigerating the sealed end of said envelope to a temperature below the boiling point of said inert gas, thereby forming a pool of liquified inert gas within said envelope; gasifying said pool of inert gas while concurrently heating the unsealed end of said envelope to soften the glass and press sealing the softened end of said envelope about a support associated with the other end of said filament.

4. The process for fabricating an incandescent lamp having a filament supported within an envelope having generally regular and smooth outer surfaces, the steps which comprise: flowing an inert gas through the length of a glass envelope containing a tungsten filament, thereby forming an atmosphere for preventing oxidation of metal parts contained therein; heating an end of said envelope to soften the glass and sealing the softened end of said envelope while maintaining the atmosphere of said inert gas; refrigerating the sealed end of said envelope to reduce its temperature below the boiling point of said inert gas, thereby forming a pool of liquified inert gas within said envelope; gasifying said pool of liquified inert gas and allowing the gas to pass from the envelope and blanket all metal surfaces; heating said unsealed end of said envelope to soften the glass concurrently with said gasification; sealing the softened end of said envelope when substantially all of the pool of liquified gas is gasified, thereby forming an incandensent lamp containing fill gas at a pressure of about one atmosphere.

5. The process according to claim 4 wherein the inert gas is argon.

6. The process according to claim 5 wherein the sealed end of the envelope is refrigerated by immersing it in a pool of liquid nitrogen.

7. In the process of fabricating an incandescent lamp the steps which comprise: flowing a fill gas through an open end of a glass envelope containing a filament; refrigerating a sealed end of said envelope to a temperature below the boiling point of said fill gas, thereby forming a liquified pool of fill gas therein; gasifying said pool of liquified fill gas and allowing the gas to pass through and out of said envelope, thereby blanketing said filament with said fill gas to prevent oxidation of metal parts; heating the open end of said envelope to soften the glass concurrently with the gasification of said pool of fill gas and sealing the softened end of said envelope when substantially all of the liquified fill gas is gasified, thereby forming an incandescent lamp containing fill gas at a pressure of about one atmosphere.

8. In the process of fabricating an incandescent lamp the steps which comprise: forming a pool of liquified fill gas within a giass envelope having an open end and sealed end with lead-in wires supporting a filament through said sealed end; gasifying said liquified pool of fill gas and allowing the gas to pass through and out of the open end of said envelope, thereby blanketing metal surfaces to prevent their oxidation; heating the open end of said envelope to soften the glass concurrently with said gasification and sealing the softened end of said envelope when substantially all of the pool of fill gas is gasified, thereby forming an incandescent lamp containing a fill gas at a pressure of about one atmosphere.

9. In the process of fabricating an incandescent lamp the steps which comprise: flowing a fill gas through the open end of a glass envelope containing a filament; refrigerating a sealed and of said envelope to a temperature below the boiling point of said fill gas, thereby forming a pool of liquified fill gas therein; gasifying said pool of liquified fill gas and allowing the gas to pass through and out of said envelope, thereby blanketing said filament with said fill gas to prevent its oxidation; heating the open end of said envelope to soften the glass concurrently with said gasification of said fill gas and sealing said softened end of said envelope when substantially all of said pool of liquified fill gas is gasified.

10. In the process of fabricating an incandescent lamp the steps which comprise: flowing an inert gas through the open end of a glass envelope containing a filament; refrigerating a sealed end of said envelope to a temperature below the boiling point of said inert gas, thereby forming a pool of liquified inert gas therein; gasifying said pool of liquified inert gas and allowing the inert gas to pass through and out of said envelope, thereby blanketing said filament with said inert gas to prevent its oxidation; heating the open end of said envelope to soften the glass concurrently with the gasification of said inert gas; sealing the softened end of said envelope when substantially all of the pool of inert gas is gasified thereby forming an incandescent lamp containing a filling of inert gas at a pressure of about one atmosphere.

11. The process according to claim 10 wherein the inert fill gas is argon.

12. The process according to claim 11 wherein the sealed end of the envelope is immersed within a bath of liquid nitrogen.

References Cited by the Examiner UNITED STATES PATENTS 2,417,361 3/47 Herzog 316-19 2,870,586 1/59 Pearson et al. 2,900,771 8/59 Levand 537 FRANK E. BAILEY, Primary Examiner.

LEON PEAR, Examiner. 

1. IN THE PROCESS OF FABRICATING A LAMP HAVING AN ENVELOPE OF GENERALLY REGULAR AND SMOOTH OUTER SURFACES THE STEPS WHICH COMPRISE: FLOWING AN INERT GAS INTO A GLASS ENVELOPE CONTAINING A FILAMENT, THROUGH AN UNSEALED END OF SAID ENVELOPE; REFRIGERATING A SEAL END OF SAID ENVELOPE TO A TEMPERATURE BELOW THE BOILING POINT OF SAID INERT GAS, THEREBY FORMING A POOL OF LIQUIFIED INERT GAS THEREIN; GASIFYING SAID POOL OF INERT GAS AND HEATING SAID UNSEALED END OF SAID ENVELOPE TO SOFTEN THE GLASS CONCURRENTLY WITH SAID GASIFICATION; SEALING THE SOFTENED END OF SAID ENVELOPE WHEN SUBSTANTIALLY ALL OF THE POOL OF LIQUIFIED INERT GAS IS GASIFIED, THEREBY FORMING AN INCANDESCENT LAMP CONTAINING A FILLING OF INERT GAS AT A PRESSURE OF ABOUT ONE ATMOSPHERE. 